Among processes for forming an SOI (Silicon on Insulator) wafer, there has been, for example, a process in which silicon wafers are bonded to each other with an oxide film interposed therebetween, followed by rendering one silicon wafer to be a thin film. In a case where a semiconductor thin film is formed on a base wafer, not limiting to such an SOI wafer, there can be adopted a method in which a semiconductor wafer and a base wafer are bonded to each other. A so-called smart-cut method (a registered trade mark) described in Japanese Laid-Open Patent Publication No. 05-211128 has been available among methods in which after a semiconductor wafer and a base wafer are bonded to each other in this way, the semiconductor wafer is rendered to be a thin film to thereby prepare a bonded wafer.
A manufacture of a bonded SOI wafer according to the so-called smart-cut method goes this way, for example: At first, a bond wafer 31 providing an SOI layer as shown in (a) of FIG. 11 and a base wafer 32 serving as a support are prepared and an oxide film 33 is formed on at least one of the wafers ((b) of FIG. 11). In (b) of FIG. 11, there is shown a case where the oxide film 33 is formed on the bond wafer 31. At least one kind of a hydrogen ion, a rare gas ion and a halogen ion is implanted into the bond wafer 31 on which the oxide film is formed to form an ion implanted layer 41 ((c) of FIG. 11). The surface of the bond wafer 31 near which the ion implanted layer 41 is formed is closely bonded to the base wafer 32 with the oxide film 33 interposed therebetween to form a bonded dual wafer 34 ((d) of FIG. 11) and thereafter a heat treatment is applied thereto to cause the bond wafer 31 to be separated at the ion implanted layer 41 to form an SOI layer 40, thereby forming a bonded SOI wafer 39 and a residual wafer 38 ((e) of FIG. 11).
Note that a heat treatment and wafer recovery in a step of separating the bond wafer 31 has been conventionally performed in the following way: At first, as shown in FIG. 12A, the bonded dual wafers 34 are erected in holding grooves 30a formed on a boat 30 at angles in the range of from 90 degrees to an angle of the order of 80 degrees relative to the boat 30. Then, the boat 30 is, as shown in FIG. 12B, placed in a horizontal heat treating furnace 35 to conduct a heat treatment at a temperature in the range of from 400 to 600° C. on the bonded dual wafers 34 and to form bonded SOI wafers 39 and residual wafers 38 and thereafter, rear surfaces 39a of the bonded wafers 39 are, as shown in FIG. 12C, sucked with a vacuum pincette 36 to recover the bonded SOI wafers 39 from the boat 30.
In a conventional method, when the vacuum pincette 36 was brought into contact with a rear surface 39a of a bonded SOI wafer 39, a case arose where a defect, deficiency and contamination occurred on the rear surface 39a by pushing with the vacuum pincette 36. Furthermore, when a bonded SOI wafer 39 was taken out, opposed surfaces of a bonded SOI wafer 39 and a residual wafer 38 separated by a heat treatment were rubbed against each other, having also led to a case where a defect and deficiency occurred on a separation surface 39b of the bonded SOI wafer 39. Since the boat 30 and the bonded dual wafers 34 were in contact with each other in the holding grooves 30a at end surfaces of the bonded dual wafers 34, defects, deficiency and the like occurred at the end surfaces thereof by a shock when the bonded dual wafers 34 each obtained by bonding both wafers to each other at room temperature are placed on the boat 30, or when the bonded SOI wafers 39 were recovered even after formation of the bonded SOI wafers 39, having led to a case where defects in products were provoked. Conventionally, since the above process was conducted manually, a problem occurred that neither a defect, deficiency, contamination and the like were sufficiently prevented nor a sufficiently high: productivity was assured. Such problems are not specific to a bonded SOI wafer and occur similarly in cases of other bonded wafers each of which were obtained by bonding a semiconductor wafer and a base wafer to each other as far as the above process was adopted.
It is an object of the invention to provide a method for manufacturing a bonded wafer in which not only is suppression realized on occurrence of a defect, deficiency and contamination when separated bonded wafers are taken out in a method for manufacturing a bonded wafer according to a so-called smart-cut method, but also automation suitable for mass production is enabled.